In fuel cells, a fuel and an oxidant are supplied to two electrically-connected electrodes to electrochemically oxidize the fuel, thereby converting chemical energy directly to electrical energy. Accordingly, fuel cells are not limited by the Carnot cycle and show high energy conversion efficiency. A fuel cell is generally composed of a stack of fuel cells, each of which has an electrolyte membrane that is sandwiched by a pair of electrodes, i.e., a membrane electrode assembly, as the basic structure.
Platinum and platinum alloy materials have been used as electrode catalysts of the fuel electrode (anode electrode) and oxidant electrode (cathode electrode) of a fuel cell. However, platinum in an amount that is required of electrode catalysts using the latest technology, is still too expensive to make the commercial mass production of fuel cells possible. Accordingly, there has been considerable research on the reduction of the amount of platinum contained in the fuel and oxidant electrodes of a fuel cell by combining platinum with a less expensive metal.
In recent years, as a fuel cell electrode catalyst, core-shell catalyst particles have attracted attention. For example, in Patent Document 1, a method for producing carbon-supported core-shell catalyst particles including a core and a shell covering the core, is disclosed, the method including a step of preparing fine core particles supported on a carbon support, an inactivation step of inactivating functional groups present on the surface of the carbon support by mixing the fine core particles with an inactivator, and a step of covering each fine core particle (core) with the shell after the inactivation step.